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Fuel Economy Rating:

The 12-cylinder S600 notwithstanding, the S-class is relatively efficient for something weighing in excess of 5000 pounds. The plug-in hybrid tops the range with a 26-mpg combined rating from the EPA, while the rear-wheel-drive, V-8–powered S550 carries a 21-mpg combined estimate (all-wheel drive drops that figure to 20 mpg). In our testing, the S550’s highway fuel economy is quite good. We have not formally tested an S600, but its 16-mpg combined rating from the EPA says pretty much everything you need to know about its efficiency or lack thereof.

Fuel Economy Ratings Compared: 2017 Mercedes-Benz S550

Fuel Economy Ratings Compared: 2017 Mercedes-Benz S550e

Fuel Economy Ratings Compared: 2017 Mercedes-Benz S600

We’ve devised our own fuel-economy test in an attempt to replicate how most people drive on the highway. Our procedure entails a 200-mile out-and-back loop on Michigan’s I-94 highway. We maintain a GPS-verified 75 mph and use the cruise control as much as possible to mimic the way many drivers behave during long trips.

A 2017 S550 eked out an incredible 27 mpg on our highway test loop. (More incredible still, that figure is only so-so when compared with other large, powerful luxury sedans.) Although we have not tested an S550e on our highway loop, a 2015 model on which we gathered mixed-driving fuel-economy data scored 20 mpg; the same S550 that nailed 27 mpg on the highway test averaged a mere 15 mpg in similar mixed driving. Essentially, the hybrid and its 12 miles of electric-only driving range might be favorable to owners who spend their time in city traffic—where the electric assist does more to cut fuel use than it does on the highway—while long-distance cruisers will appreciate the S550’s V-8 thrust and long-legged freeway efficiency.

Test Results: Highway Fuel Economy

Between the S550’s 27-mpg highway efficiency and 23-gallon fuel tank, it can travel 620 miles per fill-up, tops among its closest competitors.